System for automatically plotting sensitometric control strip deviations



Apnl 12, 1966 H. DEVEREAUX, JR 3,246,334

SYSTEM FOR AUTOMATICALLY PLOTTING SENSITOME'TRIC CONTROL STRIP DEVIATIONS Filed March 9, 1964 4 Sheets-Sheet 1 DENSITY (X- AXIS) O .2 .4 .6 .8 L0 L2 L4 L6 L8 2.0 2.4 3.0 3.6 4.0

FIG. 3.

IN VEN TOR.

ATTORNEY.

HARRY L. DEVEREAUX, JR

ff/44m April 12, 1966 H. DEVEREAUX, JR 3,

SYSTEM FOR AUTOMATICALLY PLOTTING SENSITOMETRIC CONTROL STRIP DEVIATIONS Filed March 9, 1964 4 Sheets-Sheet 2 so V MANUAL DENSITOMETER FILM DRIVE UNIT PHOTO CELL INTERNAL SIGNAL MODIFING CIRCUITY FIG. 6. I COMPARATOR .1.

| 50 x-Y" PLOTTE LOGARITHMIC CONVERTER f UNIT 1/ l3 '4 II II I ll V T 5|z 5m INVENTOR. HARRY L. DEVEREAUX,JR.

ATTORN EY.

April 1966 H. L. DEVEREAUX, JR 3,246,334

SYSTEM FOR AUTOMATICALLY PLOTTING SENSITOMETRIC CONTROL STRIP DEVIATIONS Filed March 9, 1964 4 Sheets-Sheet 3 MODE SWITCH 3 10 i 'l 5la B .1. I RL 0 o s1 INVENTOR. R HARRY L. DEVEREAUXJ FIG. 7A. BY

ATTORNEY.

April 12, 1966 H. DEVEREAUX, JR 3,246,334

SYSTEM FOR AUTOMATICALLY PLOTTING SENSITOMETRIC CONTROL STRIP DEVIATIONS Filed March 9, 1964 4 SheetsSheet 4 2 l (STEP uuusen) 50 GREEN 53 l i i e1 51mm swn'cu 68 i MOTOR RED //54 I STEP RESET 6 6 1, A A A SIGNAL SIGNAL I FILM srmp BLUE nmve unnfss l i 6 5 5 6 6 i I? u T marmc I I I0 -56 I ML L 3 J; 4% A A A CONVENTIONAL MANUAL PICTOR'AL DENSITOMETER LOGARITHMIC NVERTER co uun' A 6 6 6 6 J Fad ll 58 r L I 52 ap T PLOTTER um'r 52' INVENTOR. HARRY L. DEVEREAUX,JR. FIG. 78.

ATTORNEY.

United States Patent 3,246,334 SYSTEM FOR AUTOMATICALLY PLBTTKNG SEN- SITOMETRIC CONTROL STREP DEVIATEUNS Harry L. Devereaux, Jr., China Lake, alif., assignor to the United States of America as represented by the Secretary of the Navy Filed Mar. 9, 1964, Ser. No. 350,621 Claims. (Cl. 346-49) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to automated systems for plotting optical density curves, for photographic process control test strips, and more particularly to an improvement which accommodates a plotting of test strip density deviation from a preselected standard density curve for a particular photographic process.

One of the basic tools utilized in a photographic processing laboratory for measuring product quality and stability or uniformity of processing from hour to hour is the sensitometric process control test strip. The strip normally consists of twenty-one steps of uniformly increasing exposure areas, which, after photographic processing, are nearly transparent at one end and almost opaque at the other with steps of increasing density occurring between the strips ends. Normally, the density of each step is determined and plotted to produce an S-shaped curve, commonly referred to throughout the industry as the characteristic or H and D curve of the specific film-process, or emulsion process, combination. In the case of a black and white process, only one curve, produced utilizing white light, is required to characterize the emulsion-process combination. With a color process, three approximately superimposed curves are normally produced, utilizing red, green, and blue light to represent the density values of each step of the strip to the various colors of light. These curves are then compared to a standard curve to acquire test strip density value deviation with respect to a plurality of predetermined values are represented by the standard curve.

At present, the vast majority of film processing facilities utilize manually operated systems, which require that a given test strip be drawn by hand through a densitometer, step-by-step, density value readings taken for each step of the test strip, sequentially recorded, plotted, and then compared to a standard curve for purposes of determining test strip density deviation from the standard curve.

Such systems have been successfully automated in part, as disclosed in applicants copending application Serial Number 244,841, filed December 14, 1962, now Patent No. 3,141,727, however, such systems lack the capabilities of automatically comparing obtained density values with a predetermined standard.

Therefore, the general purpose of the instant invention is to provide a simple system utilizing a comparator unit in combination with a system of the type disclosed in the aforementioned co-pending application, which comprises a fully automatic system capable of rapidly determining and plotting test strip step density value deviations from predetermined values or a curve established by a standard density strip, whereby the system is adaptable to readily provide intelligence heretofore obtainable only through lengthy and tedious operations carried out by highly skilled personnel.

An object of the instant invention is to provide a fully automatic system capable of providing and plotting test strip density value deviations, in a photographic process, from a preselected standard density curve.

Another object is to provide a system capable of substantially reducing the time required in plotting step density deviations from a preselected standard density for a test strip fed through a densitometer.

A further object is to provide a comparator circuit capable of providing predetermined output signals to a plotting unit in a test strip density curve plotting system.

Still a further object is to provide a variable, simple, and economic system having the capabilities of rapidly providing and plotting deviations for test strip step density values, with respect to preselected values, and which may be rapidly operated by relatively unskilled personnel to provide intelligence heretofore necessitating extensive operations performed by highly skilled personnel.

Other objects, advantages and novel features of the invention will becofne apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a partial perspective view of the over-all system of the present invention;

FIG. 2 is a fragmentary view of a portion of a typical test strip of the type analyzed by the system of the instant invention;

FIG. 3 illustrates two typical curves as may be plotted by the system of the instant invention;

FIG. 4 is a partial elevation of the test strip drive unit shown in FIG. 1, on an enlarged scale, illustrating a camand-switch arrangement for various microswitches as provided for in the instant invention;

FIG. 5 is a side elevation, taken at 5 in FIG. 4, illustrating a cam arrangement for various cams;

FIG. 6 is an over-all schematic view of the system of the present invention; and

FIGS. 7A and 7B together comprise a diagrammatic view of the comparator circuit of FIG. 6.

Referring more specifically to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a combination of units, which go to make up the basic combination of the present invention. As more clearly described in applicants aforementioned application, the basic system comprises a base B having mounted thereon a densitometer 10, of known design, such as, for example, the commercially available Westrex 1100 manual densitometer, which is provided with a logarithmically responsive visual aid or meter 10'. The densitometer is utilized to determine and indicate a density value for each step 11 of a test strip 12, more clearly shown in FIG. 2, which values may be converted to electrical signals and directed to a logarithmic converter 13. Since densitometers are well known and various types are commercially available, it is to be clearly understood that the hereindescribed arrangement of densitometer 10 and converter unit 13 merely serves to illustrate one arrangement that may be used to practice the instant invention, particularly since some of the commercially available densitometers effect internal logarithmic conversion of their photocell output signals.

The converter 13 utilizes the electrical signals to dictate an output signal indicative of the optical density of each step 11 of the film strip 12. As disclosed in the aforementioned application, the converter 13 is of known design, and is commercially available under the trade name Mosley Model 603 logarithmic converter.

The output signal from the converter 13 is fed into an X-Y plotter 14 having a plotting pen 15 and a conven tional drive means 14', for driving the pen in an X direction and means 14" for driving the pen in a Y direction, FIG. 6, to plot a curve C, FIG. 3, on a graph G.

A test strip guide track 16 is provided for guiding a test strip 12 through the densitometer as it is advanced by a drive unit 17 including a flexible draw-line 18 secured to the strip by a suitable clip 19. The operation of the system is more clearly set forth in the aforementioned copending application. However, it is to be understood that the drive unit 17 comprises a housing 21, mounted on the base B, for confining a structural support base 22 having integral vertical support members 22' extending vertically therefrom and serving as a support for various drive unit components, including a take-up reel assembly 23, an assembly-connected drive motor 24, and a linear single-turn potentiometer 25.

The reel assembly 23 is provided with a circumferentially grooved disk or sheave 26 to which one end of the draw-line 18 is secured, and about which the draw-line is Wound as the sheave is driven through a drive shaft 27, a friction clutch utilizing a felt layer 28 and a clutch plate 29 mounted foraxial displacement along the shaft 27. A drive dog 30 may be secured to the draft 27 to mate with a dog 30 oppositely secured to a face of the clutch plate 29 to establish a dog-type drive coupling between the shaft and clutch plate.

The felt layer 28 serves as a friction plate to engage a face of the sheave 26 to establish a friction drive relationship therebetween. The plate 22 is continuously biased toward the sheave by a compression spring 31 axially mounted about the shaft 27 with one end thereof being fixed relative to the shaft by suitable adjusting means 32, which may comprise a thread nut having spring retaining shoulders formed thereon. The shaft 27 is mounted on members 22, by suitable bearing means, and serves to transmit power from the motor 24 to the plate 29 through the dogs 30 and 30' so that as the motor 24 becomes activated the sheave 26 is caused to rotate for drawing the line 18 thereabout and drawing an attached test strip 12 toward the housing 21 along the track 16 through the densitometer 10.

At the end of the shaft 27, opposite the motor 24, there is a coupling sleeve 34, which serves to align the shaft 27 and couple sheave 26, with a potentiometer connected drive shaft 37 for driving the aforementioned single-turn potentiometer 25.

For controlling rotation of the sheave 26 and shaft 37, and consequently the operation of the potentiometer 25, the motor '24 is connected with a suitable 1l0-volt alternating current power source, not shown, through leads L, FIG. 6, including series connected microswitches MS and M8 which are fixed relative to the sheave 26. Each of the switches MS, and M5 is provided with a cam follower 39, only one of which is shown in FIG. 4, and are spring biased to a closed condition. The switches M8 and M5 are caused to open through a displacement of their cam followers under the influence of cams 41 and 41, FIG. 5, fixed to the normally rotating sheave 26 in an off-set relationship with respect to each other. Either of the cams may thus function to break the power circuit to the motor 24 by opening one of the microswitches when a predetermined rotation is imparted to the sheave 26.

Referring more specifically to FIG. 6, the power source for the potentiometer includes a 1 /2 volt D.-C. (direct current) battery V which is connected to the potentiometer 25 through one half of a double-pole, single-throw switch CS. The other half of the switch CS is connected to the lead L between the A.-C. source and the microswitch M8 so that a single motion of the switch CS will make or break the circuits for the potentiometer 25 and motor 24.

A normally open start switch SS is also provided in the power supply circuit for the motor 24 and is so arranged as to shunt microswitch M8 when closed, so that when the switch M8 is opened, by cam 41, the circuit to switch M8 may be closed for initiating an activation of the motor 24 for driving the sheave 26. When the motor 24 is thus activated, switch MS will close and start switch SS may be again opened. Once the motor 24 is activated, it serves to rotate the sheave 26 until the switch M8 is opened under the influence of cam 41'.

As the motor 24 drives shaft 27 and rotates the sheave 26, the potentiometer shaft 37 is driven for altering the output signal from the potentiometer in accordance with extent of rotation, whereby the plotting pen 15 may be driven along its Y axis in accordance with the rotation of the sheave 26. Consequently, the extent of pen displacement will be commensurate with test strip displacement so that the pens position along its Y axis on the graph G will coincide with the particular step 11 of the test strip 12 being read by the densitometer 10. Hence, it is to be understood that when the switch MS is open the pen 15 will be displaced to or near its zero or starting position 0 on graph G. Once the switch SS is closed the sheave 26 will be driven to draw the test strip 12 through the densitometer 10, whereby the pen 15 will be driven along its X axis in accordance with the signal received from the logarithmic converter 13, to establish density values for the particular step of the test strip being read, while the output signal from the potentiometer 25 serves to drive the pen 15 along its Y axis to establish the step of the strip being read. The pen 15 is thus caused to plot a curve C across the face of the graph G as signals are simultaneously fed to the plotting unit 14 from the driven potentiometer 25 and logarithmic converter 13.

Once the strip 12 has been drawn through the densitometer 10, the microswitch M8 is opened, under the influence of cam 41', causing the motor 24 to become inactivated. The operator may now remove the graph from the machine and draw the line 18 back to its starting position, accommodated by a slipping of the surface 28 relative to the sheave 26, whereupon the circuit to the motor 24 will be closed for rotating the sheave 26 sufficiently for causing cam 41 to open microswitch MS for thus repositioning the draw-line 18 at a starting position, or to a position of alignment for an aligning hole H formed in the strip 12 to indicate a proper positioning thereof.

Where desired, an adjusting means, including sheaves 48, 48' and 53, may be provided for adjusting the eifective length of the draw-line 18, so that the hole H formed in an attached test strip 12 may be accurately positioned relative to the densitometer 10 to thus establish a starting position for the test strip, as more fully described in the aforementioned application.

As hereinbefore mentioned, the hereinbefore described system fails to provide means for graphically illustrating deviations in density values with respect to a predetermined standard. The following description of the instant invention includes system modifying means which have been found to function quite satisfactorily for causing the system to provide a desired density deviation curve DC, FIG. 3, which permits the system to alternatively illustrate deviations from a preselected set of standard values, which may be fed into the system as desired.

Referring, for the moment, to FIGS. 6, 7A and 713, a comparator unit 50 having a circuit connected across the plotter input leads from the converter unit 13 through a mode switch 51 so that it is capable of altering the value of the conventer output signal to the X-Y plotter unit 14. Additionally a comparator circuit load resistor R is connected across the output leads of the converter unit 13, FIG. 7A. The mode switch 51 is provided with terminals 531,, and 51 FIG. 6. The terminal 51,, may be termed an H and D terminal as it serves to disconnect the output of the comparator unit 50 from the system when the switch 51 is open so that the system functions to plot an H and D curve in the aforedescribed manner. However, when the switch 51 is closed, the output signal. from the comparator unit 50 is added or combined with the signal from the logarithmic converter unit 13, through junction terminals 52, 52' to in effect provide a modified logarithmic converter unit input signal to the plotter unit 14.

The signals obtained from the comparator unit 50 are of predetermined values corresponding to standard density signals. As a test strip 12 is read, or fed through the densitometer 10, the densitometer provides signals proportional to the individual step densities and are compared to corresponding standard signals obtained from the comparator unit 50 as the signals are combined across the resistor R and fed through terminals 52 and 52' to the plotter 14. The resulting or difference signals are now directed to the pen drive means 14' of the plotter unit 14 in order to drive the pen in its X direction in accordance with the thus established difference signal. If the signals from the units 13 and 50 tend to cancel each other, the pen will not be displaced from its then present position with respect to the graphs X axis, however, if they are reduced or amplified in magnitude the pen drive means 14 will react to the change and drive the pen 15 in laterally opposite directions in accordance therewith.

The comparator unit 50 may be mounted in any suitable housing and attached to the base B. The circuit of the comparator unit '50 comprises five individual banks 513, 54, 55, 56, and 57, of voltage divider networks with each bank having an external adjusting panel, designated 53 -57, FIG. 1. Each network is capable of providing a separate comparator circuit output signal of a predetermined value, as will hereinafter be more fully explained. While the specific number of banks may be varied as found necessary or desirable to accommodate specific laboratories, the banks utilized in the present invention accommodate green, red, and blue standard curves of a color process, the standard curve of a high contrast metric black and white process, and the standard curve of a lower contrast pictorial black and white process.

'Each of the five banks designated 53, 54, 55, 56, and 57, is connected to a -volt D.-C. power source B through one of five circuit parallel connected potentiometers, designated P-53, P-54, P-SS, P-5d, and P-57, and each is provided with twenty-two voltage divider net works NW connected in circuit parallel. Each network NW is, in turn, connected with a fixed pick-off terminal T through which a circuit may be established through a preselected terminal of a selector switch 58, designated 58 '58 to the mode switch 5- 1 by means of a displaceable terminal T driven in a manner hereinafter more clearly set forth.

As each of the banks 53-57 are of a similar design and function in a similar fashion, it is deemed sufficient, for purposes of understanding the invention, to describe a single one of the banks in detail. Therefore, a detailed description of banks 53, 5'4, 55, and 56 is omitted in the interest of brevity. However, it is to be particularly noted that all of the banks 53-57 are each designed to provide a separate series of standard density signals with each signal being of a magnitude differing from the magnitude of a corresponding signal obtained from each of the other banks for each step 11 of a strip '12 being read by the densitometer 10. Thus it is to be understood that it is possible to select one of five different sets of standard density signals by merely altering the position for the selector switch 58, through a selector knob 53' externally mounted on the base B, FIG. 1.

Referring now particularly to bank 57, FIGS. 7A and 7B, each voltage divider network NW comprises a plurality of series connected resistances. Since each film strip normally is provided with twenty-one steps 11, twenty-one voltage divider networks NW are provided comprising a potentiometer 60, connected in circuit series between a first fixed resistance R and a second fixed resistance R The values of resistance for each of the resistances R and R as well as the potentiometer-s, may be varied as found desirable by those skilled in the art to provide a variable output signal from each arm 61 of a voltage magnitude corresponding to a predetermined standard signal. Each arm 61 is connected with one of the fixed pick-oil terminals T hence the arm 61 of any selected network NW may be singularly connected through a selected one of the terminals of switch 58 to the resistance R The function of each of the potentiometers 60 is to provide an output signal of a predetermined value to its associated pick-off terminal T The value of the signal obtained from any one of the Potentiometers 60 may be varied by adjusting the potentiometers arm in a conventional manner. Hence, by adjusting the posit-ion of all of the arms, a series of standard signals may be obtained in sequence and combined with the signals from the logarithmic converter unit 13, as the displaceable terminal T is sequentially displaced, to provide a difference signal or modified converter input signal to the pen drive unit 14'.

Each of the banks is provided with an additional potentiometer 62, having its arms connected with a fixed terminal T and connected in circuit parallel with the aforementioned networks NW. The terminal T serves as a starting point for the displaceable terminal T and provides an output signal through the mode switch 51 to the resistance R to provide a zero reference signal to the pen drive unit when the pen 15 is at its starting position relative to the graphs X axis. Therefore, it is to be understood that each of the banks 53 57 are provided with twenty-two potentiometers and fixed pick-off terminals, whereby the displaceable terminal T must he stepped twenty-one steps from its starting position to singularly provide twenty-two output signals to be added with the logarithmic converter output signal so that the density of all twenty-one steps 11 of the test strip 12 may be compared to a predetermined standard signal.

The signals are compared in a step-by-step manner as the test strip 12 is caused to present its steps 11 at the densitometer 10. It has been found that in reading a test strip the signals obtained from the logarithmic converter 13 range between negative and positive values as the strip is read. In order to insure that the signals presented to the pen drive means 14 are of a single polarity, a one and one-half volts D.-C. power source or battery B and series connected voltage divider fixed resistance R is connected in circuit parallel with the pen drive means 1d" and units '13 and 50.

It is to be understood that the output signals obtained from the comparator circuit or unit 50 are normally of an opposite polarity from the output signals obtained from the logarithmic converter unit 13 so that each may tend to cancel the effect of the other as they are fed to the pen drive unit 14. Furthermore, when the logarithmic signals are of preselected or proper values, the signal obtained from the comparator circuit 50 for a particular step, as determined by a prior adjustment of the potentiometer 60, will be equal in value so that the effects of the two signals serve to just cancel the other, with the resulting effect that the difference signal being fed to the pen drive unit 14' is equivalent to a Zero value, so that no lateral motion is imparted by the drive means 14 to the pen 15. Consequently, no displacement along the X axis of the graph is imparted to the pen for that particular step. However, should the value of the signal dictated by the step density vary in magnitude, above or below the magnitude of the standard signal obtained from the comparator circuit 50, the ctfect of this variation will be indicated by an occurrence of lateral pen displacement, imparted to the pen 15 along the X axis of the graph G, initiated through an activation of the drive means 14'.

A row of numbered monitor or indicator lights is provided and mounted on the base B. These lights are singularly lighted in sequence to indicate the particular numbered step 11 of the strip 12 being read at the densitometer at any given moment. The row 65 may be connected across any suitable source of potential and have a circuit completed therethr'ough by a driven or displaceable terminal T through a fixed terminal T The displaceable terminal is displaced in unison with the displaceableterminals T of the comparator circuit 50.

As a practical matter, in order to impart displacement to the displaceable terminals T and T a stepping switch 67, of any suitable and commercially available design, may be provided with the fixed pick-01f terminals T T and T and the displaceable terminals mounted therein. The switch 67 is of a type which includes a mechanism or stepping switch motor 68, as schematically shown in FIG. 7B, which, upon being activated, will advance the displaceable terminals into contact with the next-in-line, fixed pick-off terminal and then become inactivated. The stepping switch is activated through a normally open microswitch M8 mounted on supports 22 adjacent the sheave 26, and is provided with a spring-biased cam follower 69. The switch M8 is sequentially closed by stepping earns 70, mounted on the rotating sheave 26, FIG. 5, which sequentially engage and raise the follower 69. A cam 70 is provided for each step 11 of strip 12 and is mounted near the outer edge of the face of the sheave 26. The earns 70 are equally spaced from' each other at distances which coincide with the spacing of the steps 11 of the test strip 12, so that as the sheave 26 causes the strip to be advanced through one step, a space between two earns 70 is traversed as the sheave rotates with respect to the cam follower 69. Hence, it is to be understood that the stepping motor 68 is activated once upon an advance of the strip 12 through one step 11. As the motor 68 is activated, each of the displaceable terminals T and T are displaced to a next-in-line pickoff terminal so that a next-in-line monitor light of row 65 will be lighted and a comparator signal representing a standard signal, for the particular step 11 of the test strip 12 being read, may be directed through the selector switch 58 and mode switch 51 to be added with the output signal of the logarithmic converter unit 13 and fed to the pen drive means 14' of the plotter unit, for the purposes hereinbefore described.

As the last-in-line step 11 of test strip 12 is advanced to be read by the densitometer 10, the microswitch M8 is activated for displacing the terminals T and T to their last-in-line pick-off terminals, whereupon the motor 24 is inactivated under the influence of cam 41'.

Where desired, the stepping switch 67 may be re-set to its starting or initial position by manually rotating 8. housing-mounted knob 68 to reposition terminals T and T to their first-in-line fixed pick-off terminals. As a practical matter, it may be found desirable to utilize a conventional electrical-manual reset switch in lieu of the type employing a knob 68, as shown in the drawings. However, as the draw-line 18 is to be drawn from the sheave 26 to reposition clip 19 at a starting position, the sheave 26 will be caused to rotate as the drawline 18 is repositioned, as hereinbefore described. This rotation may be utilized to initiate a resetting of the terminals T and T through the use of an additional microswitch or reset microswitch MS, mounted adjacent the sheave 26. The reset microswitch M8 is provided with a cam follower or lever 71 extending into the path of a reset cam 72 mounted on sheave 26. The reset microswitch M8 upon being activated through a displacement of the follower 71 by the cam 72, upon rotation of the sheave, serves to initiate a resetting of the terminals T and T of the stepping switch 67 in a conventional manner. it is to be noted that a cycle of operation will be completed with a single revolution of the sheave 26, therefore the various microswitches are actuated only once per test strip reading. Accordingly,

the sequence of operations of the system may be readily controlled by the radially off-set cams without incurring undesired switching.

Calibration of the system may be summarized as follows:

In order to calibrate the system to'provide a density deviation curve DC, FIG. 1, for a given test strip, it is first necessary to reset displaceable terminal T to contact the fixed pick-off terminal T and terminal T to contact a first-in-line terminal T or to an initial starting position representing the zero step for the test strip 12. The mode switch 51 is now closed. A control strip to be used as a standard is positioned at zero, or its starting step, at the reading aperture of the densitometer 10, and the selector switch 58 is adjusted to close a circuit between a selected bank, corresponding to the se lected test strip, and the mode switch 51. The test strip 12 is now manually positioned so that the first step of the test strip will be read by the densitometer and the stepping switch is now advanced once so that terminal T is caused to contact the next-in-line pick-off terminal T of the first network NW, and the first monitor light is lighted by a displacement of terminal T to complete a circuit therethrough. Since the output from the logarithmic converter unit is dictated by the density of a step for a standard test strip, the potentiometer 60 for the first network NW may now be adjusted, at the external panel, so that a zero voltage drop is experienced across the load resistor R This procedure may be repeated step-by-step through step twenty-one. Upon completion of the adjustment of all network potentiometers 60, the adjustment may be checked by merely reading the standard test strip with the system. If the calibration is correct, the resulting curve DC, of graph G, will be a straight line indicating no deviation. This process may now be repeated for each of the remaining banks as desired. With the systems thus calibrated, the operation thereof may be summarized as follows:

A desired one of the banks of voltage divider networks NW is selected by positioning the switch 58. The mode switch 51 is now closed. The drive unit 17, draw-line 18, and an attached test strip 12 are positioned at their initial or starting positions, as described in the aforementioned copending application. The pen 15 is positioned relative to the graphs X axis, in accordance with the null signal resulting from the combination of signals derived from potentiometer 62, of the comparator circuit 50, and logarithmic output signal derived from converter 13. The motor 24 may now be energized to rotate sheave 26, by closing switch SS, to thus initiate the systems operation.

As the motor 24 rotates to displace the first step 11 of the test strip 12 to a reading position in densitometer 10, the first-in-line cam serves to activate microswitch M8 by lifting the follower 69, whereupon the displaceable terminal T is displaced to contact the first-in-line network pick-off terminal T and the displaceable terminal T is displaced to contact the next-in-line, or step one terminal for the row of monitoring lights 65, to cause that light to be lighted, for thus indicating that the first step 11 of the test strip 12 is now being read. Simultaneously therewith, the pen 15 is driven along the Y axis of the graph G, by the pen drive means14" responding under the influence of the potentiometer 25, to its step one position.

As the terminal T contacts the first fixed pick-off terminal of the network NW represent-ing step one, a reference or standard signal is directed from the potentiometer 6%) through the mode switch 51 and is added to the density dictated signal obtained from the logarithmic converter unit 13. The difierence signal, or altered logarithmic signal, is now directed to the pen drive unit 14 of the plotter unit. Assuming that the first step 11 of the test strip being read is of a proper value, the comparator output or standard signal and the density dicta-ted out- 9 put signal from unit 13 will just cancel, whereupon pen 15 will not experience lateral displacement along the X axis of the graph. However, if the density dictated signal is of a greater or lesser magnitude than the magnitude of the standard signal, the pen 15 will be driven in accordance with the difference signal in a lateral direction along the X axis of the graph.

As the sheave 26 is continuously rotated through one revolution, the terminals T and T are sequentially displaced from their starting positions at terminals T and T in unison with test strip displacement through twentyone steps, whereby the pen 15 is thus displaced to plot the deviation curve DC on the graph G as it is driven along the graphs Y axis through twenty-one steps, and along the X axis in accordance with successive twentyone difference signals, or modified logarithmic output signals, obtained by combining the output signals from the units 13 and 50.

In accordance with the foregoing description, it is to be understood that there has been provided a simple, economic system for automatically plotting deviations in test strip step densities, which readily may be employed by relative inexperienced personnel to rapidly provide intelligence, heretofore requiring a series of tedious operations performed by highly-trained personnel.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A system for plotting a density deviation curve for a stepped process control test strip comprising in combination:

a densitometer for separately determining the density of each step of a series of steps for a process control test strip fed thereto and for providing a series of output signals indicative of the densities of succes sive steps of said test strip;

a logarithmic converter unit connected with said densitometer for receiving output signals from said densitometer and for providing a plurality of converter output signals, each having an operative potential value dictated by an output signal provided from said densitometer;

a converter-connected plotting unit, including a plotting pen and drive means therefor, for displacing said pen in opposed first and second directions in accordance with the operative potential values of the converter output signals received from said converter unit;

a continuously driven test strip drive unit operatively connected with the plotting unit adapted to sequentially displace the steps of said test strip through said densitometer and to concurrently displace the plotting pen of said plotting unit in a third direction in unison with the displacement of the test strip for indicating test strip step displacement;

a reference signal generating comparator circuit connected between the logarithmic converter uni-t and said plotting unit adapted to add reference signal potential values with the potential values of each of said converter signals to initiate modification thereof, whereby the pen of said plotting unit may be driven in its first and second direction in accordance with converter output signal potential values, as modified by said reference signal potential values; and

means connecting said comparator circuit with said test strip drive unit for sequentially activating said comparator circuit concurrently and with the displacement imparted to said test strip to provide a series of reference signals, whereby deviations from a predetermined displacement of said pen may be detected and plotted for each step of said test strip as it is displaced through said densitometer.

10 2. A system for plotting a density curve for a stepped process control test strip, means comprising in combination:

a curve plotting device including a plotting pen and a 5 pen drive means connected with said pen for selectively driving the pen in a plurality of opposite directions;

a test strip-receiving densitometer for sequentially providing a plurality of electrical densitometer output control signals, each having an operative potential dictated by the density value of a selected step of a test strip as it is fed to said densitometer;

a plotting device input circuit connecting said plotting device with said densitometer for directing said control signals to said drive means, whereby said plotting pen is driven in preselected directions in accordance with the operative potential of said densitometer output control signals;

a draw-line including means for connecting a test strip thereto;

a driven sheave connected with said draw-line;

an electrically driven motor connected with said sheave being adapted to be selectively activated for imparting rotation to said sheave for drawing a drawline connected test strip through said densitometer;

a plurality of equally spaced cam members fixed to said sheave, each being angularly displaced with respect to the other at distances dictated by the displacement distances of individual steps of the test 80 strip;

a stepping switch including a time delay means mounted adjacent said sheave adapted to be sequentially activated by said cams as said sheave is rotated by said motor;

a comparator circuit adapted to be selectively activated to sequentially provide a plurality of electrical comparator output signals each having a predetermined operative potential value;

means connecting said stepping switch with said comparator circuit for selectively activating the circuit to sequentially provide said comparator output signals as said sheave is sequentially rotated; and

an adding circuit including a normally closed mode switch connecting said comparator circuit with the plotting device input circuit, whereby output signals from said comparator circuit may be selectively added with the densitometer output control signals for providing a plurality of modified densitometer output control signals for driving said plotting pen in accordance with the operative potential values thereof.

3. The system of claim 2 wherein said comparator circuit includes:

a plurality of banks of parallel connected signal output voltage divider networks whereby, each bank is adapted to provide a plurality of comparator output signals;

a selector switch;

bank connecting means singularly connecting each of said banks of networks with one of a plurality of output terminals of the selector switch; and

means for selectively and singularly connecting said output terminals of said selector switch with said :mode switch.

4. The system of claim 3 wherein each bank of voltage divider networks further includes:

a plurality of fixed network output terminals each being singularly connected with a voltage divider network;

a displaceable terminal adapted to successively contact 7 each of said fixed terminals;

means operably connecting said displaceable terminal with said stepping switch, whereby said displaceable terminal may be selectively displaced in sequence between said network output terminals as said sheave is rotated; and

1 i 12 means connecting said displaceable terminal with said References Cited by the Examiner bank connecting means. 5. The system of claim 4 wherein each network of said UNITED STATES PATENTS plurality of voltage divider networks comprises: 2 925 2/1961 Armbrecht et a1 88 14 a series circuit including a pair of electrical resistances 5 3096137 7/1963 Silard X and an electrical potentiometer disposed therebei 3141727 64 g i 29 tween; and circuit means connecting the fixed network output ter- LOUIS J CAPOZI Primary Examiner rninal with the arm of said potentiometer. 

1. A SYSTEM FOR PLOTTING A DENSITY DEVIATION CURVE FOR A STEPPED PROCESS CONTROL TEST STRIP COMPRISING IN COMBINATION: A DENSITOMETER FOR SEPARATELY DETERMINING THE DENSITY OF EACH STEP OF A SERIES OF STEP FOR A PROCESS CONTROL TEST STRIP FED THERETO AND FOR PROVIDING A SERIES OF OUTPUT SIGNALS INDICATIVE OF THE DENSITIES OF SUCCESSIVE STEPS OF SAID TEST STRIP; A LOGARITHMIC CONVERTER UNIT CONNECTED WITH SAID DENSITOMETER FOR RECEIVING OUTPUT SIGNALS FROM SAID DENSITOMETER AND FOR PROVIDING A PLURALITY OF CONVERTER OUTPUT SIGNALS, EACH HAVING AN OPERATIVE POTENTIAL VALUE DICTATED BY AN OUTPUT SIGNAL PROVIDED FROM SAID DENSITOMETER; A CONVERTER-CONNECTED PLOTTING UNIT, INCLUDING A PLOTTING PEN AND DRIVE MEANS THEREFOR, FOR DISPLACING SAID PEN IN OPPOSED FIRST AND SECOND DIRECTIONS IN ACCORDANCE WITH THE OPERATIVE POTENTIAL VALUES OF THE CONVERTER OUTPUT SIGNALS RECEIVED FROM SAID CONVERTER UNIT; A CONTINUOUSLY DRIVEN TEST STRIP DRIVE UNIT OPERATIVELY CONNECTED WITH THE PLOTTING UNIT ADAPTED TO SEQUENTIALLY DISPLACE THE STEPS OF SAID TEST STRIP THROUGH SAID DENSITOMETER AND TO CONCURRENTLY DISPLACE THE PLOTTING PEN OF SAID PLOTTING UNIT IN A THIRD DIRECTION IN UNISON WITH THE DISPLACEMENT OF THE TEST STRIP FOR INDICATING TEST STRIP STEP DISPLACEMENT; A REFERENCE SIGNAL GENERATING COMPARATOR CIRCUIT CONNECTED BETWEEN THE LOGARITHMIC CONVERTER UNIT AND 